The present application claims the priority of Japanese Patent Application No. 2000-309327, which was filed in Japan on Oct. 10, 2000, the entire contents of which is hereby incorporated herein by reference.
1. Field of the Invention
The present invention applies to a magnetic film-forming device and method, and in particular, to a magnetic film-forming device and method which is applied in the production of giant magnetoresistive (GMR) heads and the like which have excellent magnetic film characteristics.
2. Discussion of Related Art
The formation of magnetic film is important in the manufacture of magnetic recording media such as hard disks and magnetic heads. When such magnetic films are formed it is preferable to form a film in which the magnetism can easily be changed to a specific direction. This will be explained below for the example of a magnetic head.
The surface recording density of hard disk devices (HDD) has improved at an astonishing rate in recent years. At present, surface recording densities of 20 to 35 Gbits/inch2 are being achieved and it is said that by the year 2002 this will become 80 Gbits/inch2 and 100 Gbits/inch2 in the future. Reasons for this improvement in surface density are considered to be the fact that the elements of the recording media and magnetic head are converted to thin film, and the gap between the magnetic head (recording head and playback head) and the magnetic recording medium is reduced. With regard to the development of such playback heads, in order to further improve the surface density, there has also been progress in the development of the present GMR (giant magnetoresistive) heads into TMR (tunneling magnetoresistive) heads.
The films which form the elements of the GMR head and TMR head are respectively called GMR film and TMR film. The structures of the GMR film 101 and TMR film 102 are shown in outline in FIGS. 11(A) and 11(B). These films 101, 102 have a multilayer film structure of what is referred to as the spin bulb type in which an extremely thin nonmagnetic layer 103 or an insulator layer 104 is sandwiched between two magnetic layers (a pin layer 105 with a fixed direction of magnetization and a free layer 106 whose direction of magnetization is determined by an applied external magnetizing force). In other words, the multilayer film structure of the spin bulb type makes use of a phenomenon in which the resistance is changed by means of the direction of the magnetization of the magnetic film due to different magnetic properties of the two layers (magnetoresistive effect or MR effect), and is structured in such a way that the direction of magnetism of only one of the two layers changes as a result of a change in the external magnetizing force. For example, the direction of magnetization of a magnetic layer (pin layer 105) which contacts an antiferromagnetic layer 107 such as FeMn, on top of a magnetic layer is fixed and another magnetic layer (free layer 106) is placed in a state in which it cannot adopt a particular direction of magnetization. It is to be noted that the uppermost layer of the GMR film 101 and TMR film 102 is in any case formed as an antiferromagnetic layer 107.
When a magnetic field which is generated from the magnetic recording medium is applied to the multilayer film structure part, the direction of magnetization of the free layer 106 is changed in accordance with the direction of that magnetic field and the electrical resistance of the element film changes. In the GMR head 101, an electric current is made to flow in the inward direction using Cu in the nonmagnetic layer 103. In contrast, in the TMR head 102, an insulator film 104 such as Al2O3 is used as the nonmagnetic layer and when a current is made to flow in the vertical direction of the element film, the resistance value changes and this can be used as playback output.
FIG. 12 is an enlarged view of the main film structures of a magnetic head (GMR head) seen from the underside. A coil 203 formed from Cu is provided on top of a lower magnetic pole (upper shield) 202, and an upper magnetic pole 204 is provided on the coil 203. In a multilayer film 206 in which a portion 205 is shown enlarged, a recording gap (Al2O3) 207 is formed between the lower magnetic pole 202 and the upper magnetic pole 204, an intermediate film 208 is formed on both sides of the upper magnetic pole 204, and a protective film 209 (Al2O3) is formed on the intermediate film 208. In addition, a substrate-protecting film 211 is formed on a substrate 210 and a lower shield 212 is formed on the substrate-protecting film 211. A playback element (GMR film) 214 is formed in the center on top of the lower shield 212 with the interposition of a playback lower gap (Al2O3) 213. A hard bias 215 is provided on both sides of the playback element 214. An electrode 216 is formed on the hard bias 215. The lower magnetic pole 202 is formed on the electrode 216, and the central playback element 214, with a interposition of a playback upper gap 217.
As mentioned above, in recent years, in order to improve the surface density it has been necessary to convert to thin film the recording gap 207 between the upper magnetic pole 204 and the lower magnetic pole 202, and the playback upper gap 217 and the playback lower gap 213 between the upper shield (lower magnetic pole) 202 and the lower shield 212. For example, in order to sandwich the playback upper gap 217 etc., it has been necessary to make the actual playback element (GMR film) 214 thinner. However, there is the problem that if the film of the playback element 214 is made thinner and the element width corresponding to the track width (W1 in FIG. 12) of the playback element 214 is sandwiched, the resistance value becomes larger.
Also, in order to improve the output characteristics, it is necessary for the rate of change of resistance (MR ratio) corresponding to the change in the magnetic field shown in the formula below (1) to become large.
MR(%)=(Rmaxxe2x88x92Rmin)/Rmin=xcex94R/Rmin=xcex94xcfx81/xcfx81xe2x80x83xe2x80x83(1)
Rmax: electrical resistance value measured in the same direction of the electric current as the change in magnetization of the element film
Rmin: electrical resistance value measured in the direction of the electric current perpendicular to the direction of the change in magnetization of the element film
xcfx81: resistivity=Rxc3x97t
t: film thickness
xcex94xcfx81: change in resistivity value
As shown in FIG. 13, the resistance value (R) is reduced as a function of the drop in pressure (base pressure) in the vacuum chamber. At this time, the rate of change of the resistance, MR, increases and an increase by 8% is obtained at 1xc3x9710xe2x88x927(1Exe2x88x927) Pa or above. Because this is the case, it is assumed that, in order to obtain a film with excellent magnetism characteristics with a high MR ratio, the resistivity value (xcfx81) of the film must be low.
As mentioned above, in order to make the element film thickness of the multilayer film structure into thin film, it is necessary to deposit the structural films to an approximate thickness of several nm with a high degree of uniformity of the thickness of the film and methods which slow down the disposition rate are adopted. However, slowing down the disposition rate makes it easy for impurities to enter the film, giving rise to a film with a high resistance value (R), in other words, a high resistivity value (xcfx81), and it is difficult to obtain a film with excellent magnetic properties as hoped. For this reason, there is a need for a magnetic film-forming device with which it is possible to obtain an extremely good vacuum.
Furthermore, MRAMs (Magnetic Random Access Memories) have aroused interest as non-volatile memories which have the large capacity of DRAMs, the speed of SRAMs and are rewritable. The basic structure of these MRAMs in transistor integrated circuits formed by means of conductor manufacturing processes is one in which the above-mentioned TMR elements and GMR elements with a large magnetoresistive change ratio are formed at specific locations corresponding to individual transistors.
The TMR elements in the MRAM structure have an approximate structure as shown in the above-mentioned FIG. 11(B), and they are formed so as to be positioned at the intersection points of the bit lines and rewritable word lines. In this configuration, when electric current is made to flow in the bit lines and rewritable word lines, the magnetization of the free layers of only those elements which receive the influence of the magnetic field from both bit lines and rewritable word lines is reversed. A xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d information item can be written as a function of whether or not the magnetization of the free layer is reversed in this way. However, if the change in direction of the magnetization of the two magnetic layers comprising the pin layer and the free layer is the same when current is made to flow in the bit lines, the resistance value drops to a minimum, and when the changes in direction of magnetization are opposed, the resistance value rises to a maximum. Therefore, the change in resistance (change in voltage) generated by causing current to flow in the bit lines and bringing about a tunnel current through the insulator film, such as Al2O3, between the two magnetic layers is detected, and in this way a xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d information item can be read.
When the MRAMs are manufactured, firstly an integrated circuit is formed on a silicon substrate using a semiconductor manufacturing process. Next, a TMR film or GMR film is formed on the substrate. In other words a sequence composed of magnetic film/insulator film/magnetic film is deposited in the magnetic film-forming device. In this process, as mentioned above, a low film resistivity value (xcfx81) is important for obtaining a film with excellent magnetic properties and a high MR ratio. To do this, it is necessary to have an extremely high vacuum in the magnetic film-forming chamber.
In a magnetic film-forming device, the substrate is usually conveyed into a cleaning chamber before the magnetic film is formed, and the formation of film is then prepared by preparatory evacuation of the cleaning chamber. After the cleaning chamber has been evacuated to a specific degree of vacuum (for example 5.0xc3x9710xe2x88x924 Pa), the gate valve between the cleaning chamber and the magnetic film-forming chamber is opened and the substrate is conveyed into the magnetic film-forming chamber. However, a large amount of gas is emitted from substrates which have been processed in order to form integrated circuits. For this reason, if the cleaning chamber is evacuated using, for example, a TMP (turbo molecular pump) with a pumping speed of 300 L/s, it usually takes 15 minutes to achieve a specific degree of vacuum of 5.0xc3x9710xe2x88x924 Pa, whereas with substrates processed as mentioned above, the time taken is 30 minutes to 50 minutes, in other words two to three times as long.
In order to overcome this problem, in the prior art, prior to deposition of the magnetic film, gas was emitted by heating the substrate, or the front face of the substrate was cleaned by generating plasma such as Ar. However, in substrate-heating methods, the substrate is heated by means of a heat source such as a heater or lamp and the adsorption gas in the moisture and the like which is adsorbed into the front face of the substrate was eliminated but metal impurities in the front face layer were not removed. Furthermore, during cleaning by means of plasma such as Ar, it was possible to remove surface materials which affect the film quality of the magnetic film such as adsorption gas molecules on the film-forming face of the substrate and surface oxides, but it was not possible to remove impurities in the reverse face.
In view of the above, a method for plasma-cleaning the reverse face of a substrate was developed and is disclosed in Japanese Laid-Open Patent Application No. H9-283459 and U.S. Pat. No. 4,962,049.
However, none of these methods has been capable of both removing adsorption gas molecules from the entirety of the substrate and removing impurities from the magnetic film-forming front face within a short time.
An object of the present invention is to overcome the above-mentioned problems by providing a magnetic film-forming device and method in which, by means of measures either before or during the deposition of magnetic film on the substrate during the manufacture of multilayer films such as a GMR film on a substrate, in particular, the emission of gas from the reverse face of the substrate is promoted, the quality of the film during the continuous substrate film-forming process is improved and stabilized, and throughput and productivity are increased and the magnetic properties are improved.
A magnetic film-forming device according to one aspect of the present invention is a device which deposits magnetic material on a substrate and forms a magnetic film, and is configured in such a way that it is provided with a mechanism which, before the magnetic film is formed, cleans either one or both of the film-forming face and reverse face of the substrate.
In the magnetic film-forming device having the configuration in which the substrate is cleaned using Ar plasma, or the like, by means of measures carried out before the formation of magnetic film on the reverse face of the processed substrate, the device is configured such that when this cleaning process is carried out, cleaning is performed by causing gas to be emitted from both the film-forming face of the front side of the substrate and from the reverse face of the substrate. By this means, it is possible to reliably maintain an extremely high vacuum in the film-forming environment of the magnetic film-forming chamber by reducing the emission of gas from the substrate during the formation of the magnetic film on the substrate. In addition, by shortening the time necessary for evacuation it is possible to achieve an extremely high vacuum in a short time. This improves the quality of the film and increases productivity.
In another aspect of a magnetic film-forming device according to the present invention in the above-mentioned configuration, a cleaning processing chamber which is provided with a cleaning device is preferably installed between a load lock chamber into which the substrate is introduced and a magnetic film-forming chamber in which the magnetic film is formed on the substrate, and the load lock chamber and the cleaning processing chamber, and the cleaning processing chamber and the magnetic film-forming chamber are respectively connected in an airtight fashion and the cleaning of the substrate and the formation of magnetic film on the substrate are carried out continuously without the substrate being exposed to the atmosphere. In this configuration, the effect of maintaining air-tightness in the chambers makes it respectively possible to maintain a high vacuum. In addition, preventing exposure to the atmosphere when carrying out the measures during the processing of the substrate contributes to maintaining a high vacuum state.
In another aspect of a magnetic film-forming device according to the present invention, the cleaning processing chamber described above is preferably provided with a high frequency power supplying device which applies high frequency power to the substrate. In the cleaning processing chamber, an Ar gas, or the like, is introduced and the substrate is cleaned by generating plasma by applying high frequency power to the gas.
In yet another aspect of a magnetic film-forming device according to the present invention, the high frequency power supplying device is preferably provided with a horseshoe-shaped insulator substrate-holding part which is capable of moving up and down. By moving the substrate-holding part which is formed by an insulator, the reverse face of the substrate which is mounted in the substrate-holding part is exposed to plasma and it is possible to clean the reverse face of the substrate.
According to another aspect of the present invention, the high frequency power supplying device is preferably provided with an insulator part which is arranged on the lower part of the substrate-holding part.
According to yet another aspect of the present invention, quartz is preferably used in the insulator substrate-holding part and the insulator.
A magnetic film-forming method according to one aspect of the present invention includes depositing magnetic material on a substrate to form a magnetic film, and before the magnetic film is formed, either one or both of the magnetic film-forming face and the reverse face of the substrate are cleaned. During this magnetic film-forming method, the reverse face of the substrate may be cleaned by means of measures carried out before the formation of magnetic film.
In another aspect of a magnetic film-forming method according to the present invention, the cleaning and magnetic film formation are preferably carried out at different places.
Furthermore, in yet another aspect of a magnetic film-forming method of the present invention, the cleaning is preferably carried out by applying high frequency power to the substrate.